Reverse magnetron having a tie ring stiffening structure for its cathode support fingers



April 29, 1969 Filed July 8, 1966 REVERSE MAGNETRON H G. E. GLENFIELD 3,441,792

AVING A TIE RING STIFFENING STRUCTURE 'Sheet FOR ITS CATHODE SUPPORT FINGERS RESONANCE PRIOR ART PRESENT INVENTION INVENTOR.

GEORGE E.GLENFIE LD FREQUENCY C.P.S.

7 BY Ada-3, A

A ORNEY April 29, 1969 E. GLENFIELD 1 REVERSE MAGNETRO N T R STIFF NG STRUCTURE FOR CAT E P FING Filed July 8, 1966 Sheet 6 of 2 IN VENTOR.

GEORGE E. GLENFIELD BY 1 we ORNEY United States Patent US. Cl. 315-3951 6 Claims ABSTRACT OF THE DISCLOSURE A reverse magnetron microwave tube is disclosed. The microwave tube includes a circular electric mode cavity resonator surrounded by an array of vane resonators coupled to the fields of the cavity resonator via an array of axially directed coupling slots communicating through the side wall of the cavity resonator. A thermionic cathode emitter concentrically surrounds the array of vane resonators for producing an electron stream for interaction with the fields of anode vane resonators. The cathode emitter is supported in concentricity with the anode vane resonators by means of a plurality of S- shaped spring fingers disposed at intervals about the outer periphery of the cathode emitter. A tubular tie ring is coaxially disposed of the cathode emitter and is fixedly secured to and circumferentially interconnects the axially directed central portions of the spring fingers to stiffen the spring supports, thereby suppressing certain mechanical resonant modes of vibration which otherwise render the tube microphonic.

Heretofore, reverse magnetrons employing spring finger support of the cathode emitter have been built. One such tube is described and claimed in US. patent application 219,702 filed Aug. 27, 1962, now issued as US. Patent 3,255,377 on June 7, 1966. and assigned to the same assignee as that of the present invention. Such spring fingers are found useful for maintaining the necessary high degree of concentricity of the anode and cathode structures during the thermal cycles encountered in tube processing and in use. However, it was found that the prior support structure, wherein the cathode was supported from essentially onliy the turned-in foot portions of the fingers, that mechanical resonances of the spring support structure were excited under vibration. Such mechanical resonances produced frequency modulation of the microwave output signal and spread the output power outside of the desired frequency band of operation.

In the present invention, the undesired mechanical resonances of the cathode spring finger support structure have been suppressed by tying the fingers together intermediate their lengths by a tie ring, thereby stiffening the support structure and pushing the mechanical resonant frequencies thereof out of the vibration band encountered in use. In a preferred embodiment, the number of support fingers has also been increased to five spaced at 60- degree intervals about the circumference of the cathode emitter.

The principal object of the present invention is the provision of a reverse magnetron microwave tube having improved performance under vibration.

One feature of the present invention is the provision of a tie ring for tying together the spring fingers of the cathode support intermediate their lengths, whereby the cathode support structure is stiffened and mechanical resonances suppressed in vibrational frequency range of interest.

3,441,792 Patented Apr. 29, 1969 "ice Another feature of the present invention is the same as the preceding wherein there are at least five spring finger supports spaced about the periphery of the cathode emitter to substantially strengthen the cathode support structure.

Another feature of the present invention is the same as any one or more of the preceding features wherein the tie ring has an axial extent substantially coextensive with the axial extent of the spring finger supports.

Other features and advantages of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein:

FIG. 1 is a perspective view of a reverse magnetron employing features of the present invention,

FIG. 2 is an enlarged sectional view of the structure of FIG. 1 taken along line 22 in the direction of the arrows;

FIG. 3 is a sectional view of the structure of FIG. 2 taken along line 33 in the direction of the arrows, and

FIG. 4 is an enlarged fragmentary sectional view of the structure of FIG. 3 taken along line 4-4 in the direction of the arrows.

FIG. 5 is a plot of displacement of the shake table versus frequency of vibration for vibration test of a tube with and without the tie ring of the present invention.

Referring now to FIG. 1 there is shown an external perspective view of a reverse magnetron tube 1 incorporating features of the present invention. The tube 1 includes a generally cylindrical central body structure 2 as of copper which contains the microwave anode circuit and cathode emitter and is evacuated to a low pressure as of 10 Torr. A 1ead-in high voltage insulator assembly 3 depends from the main body 2 to bring in the cathode voltage, as of --23 kv. A tuner housing assembly 4 is mounted on one axial end of the main bod 2 and an output circular electric mode waveguide and output window assembly 5 is mounted on the other axial end of the main body 2.

Referring now to FIG. 2 the tube will be described in greater detail. A circular electric mode cavity resonator 6 is centrally disposed of the tube main body on its central axis. The cavity resonator 6 as defined by a region bounded on the sides by a cylindrical anode wall 7 and on one end by a conductive end wall 8 and on the other end by a tuning disk 9, forming the other end wall of the cavity 6.

An array of vane resonators 11 project outwardly from the cavity sidewall 7. An array of axially directed coupling slots communicate through the side wall 7 with alternate ones of the vane resonators for locking the 1r mode of the vane resonator system to the TE mode of the cavity resonator 6. A cathode emitter ring structure 12 surrounds the vane resonator array 11 to define an annular crossed field electronic interaction region 13 therebetween. A pair of axially spaced cylindrical magnetic pole pieces 14 and 15 are disposed on opposite sides of the interaction region 13 to provide an axially directed magnetic field therethrough which is orthogonal to the electric field between the cathode ring structure 12 and the vane array 11, operating at anode potential. A pair of C-shaped magnets 16, only partially shown, are coupled to the main body 2 externally thereof for supplying the magnetomotive force to the pole pieces 14 and 15.

The 1r mode magnetron operation of the vane resonator array supplies energy to the TE cavity 6. An output circular electric mode waveguide 17 is axially disposed of the tube 1. A wave permeable vacuum tight window 18 is sealed across the waveguide 17. Output wave energy at the operating frequency of the tube, such as 35 gHz., is coupled out of the cavity 6 around the perimeter of the disk 9 and through the waveguide 17 to a suitable load, not shown. A conductive rod 19, mounted on the center line of the cavity 6, supports the disk 9 and also serves as the cavity tuner by varying the axial position of the disk 9. The rod 19 is actuated via conventiona1 means and is sealed to the tube body 2 via a gas-tight flexible bellows 21.

The cathode emitter ring structure 12 is supported from the end wall 22 of the cylindrical tube body structure 2 via a plurality of axially directed insulator assemblies 23 and spring fingers 24.

Referring now to FIGS. 3 and 4 the spring finger supports 24 will be more fully described. Five S-shaped spring fingers 24 as of 0.015" thick molybdenum sheet stock are spaced about the cathode emitter ring structure 12 at 60 intervals. Cathode current and voltages are brought into the emitter ring structure 12 via hairpin shaped leads 25. Each spring finger includes a pair of radially directed foot portions 27 and 28 one 28 of which turns out and the other 27 of which turns in. An axially directed leg portion 29 interconnects the two foot portions. In a typical example, the finger is 0.375" wide and 0.015" thick, the foot portion 27 is 0.272" long, the foot portion 28 is 0.500" long, and leg portion 29 is 0.45 long.

The cathode emitter ring structure 12 is mounted on the inwardly directed ring-like foot portion 27 by means of a set of axially directed bolts 30 as of stainless steel. The ouwtardly directed foot portions 28 are afiixed to the ends of the axially directed insulator assemblies 23, which in turn are fixedly secured to the transverse wall portion 22 of the tube body structure 2. The foot portions 28 are apertured to pass over studs 31 fixed in the ends of the insulator assemblies 23. Nuts 32 are threaded over the studs 31 to hold the spring fingers 24 in position.

A tubular tie ring 33, as of 0.010" thick molybdenum, is brazed to the inner wall surface of the axially directed leg portions 29 of the spring fingers 24. The tie ring 33 has an axial length which is axially coextensive with substantially the entire axial extent of the leg portions 29 of the fingers 24, i.e. greater than 75%. The tie ring greatly stiffens the spring finger support system against torsional distortion under certain types of vibration while still permitting the spring fingers to perform their function of maintaining a high degree of concentricity between the anode and cathode during tube processing and in use.

The cathode emitter ring structure 12, which is bolted to the ring-shaped spring feet 27, includes a ring-shaped cathode support body 35 as of molybdenum. A toroidal shaped heater cavity 36 is located in the thick portion of the support body 35. A helical heater wire 37 is wound inside the heater cavity 36 and insulated from the body 35 by four arcuate ceramic rod structures 40 as of alumina disposed at the corners of the cavity 36. A ring-shaped cover plate 38 as of molybdenum closes off the top of the heater cavity 36. An axially flanged heat shield ring 39 as of 0.010" thick molybdenum, is disposed over the top of the cathode support body 35. The axial flange portion 41 of the shield 39 makes a close mechanical fit with the inside surface of the tie ring 33. The ringshaped foot 27 of the spring fingers 24 forms a lower heat shield, and both the upper heat shield 39 and the lower shield 27 are spaced from the cathode support body 35 via 0.010" thick molybdenum washers 42 to reduce thermal leakage from the cathode heater. The bolts 30, which hold the emitter ring structure to the spring fingers, pass axially of the tube through holes in the heat shields 39 and 27, spacers 42 and heater support body 35. The bolts 30 are threaded into tapped holes in a boss ring 43 for pulling the assembly together.

A cathode thermionic emitter ring member 44, as of porous impregnated tungsten, is brazed to the inner end of the thin portion of the heater support body 35. A pair of cathode end heat rings 45 overlay the axial ends of the emitter ring 44 and are held to the heater body 35 via screws 46.

During manufacture of the tube 1 the cathode ring structure 12 is assembled on the spring fingers 24. The subassembly is then enclosed in a vacuum bell jar and heat cycled to remove any residual stress or imported :stress as a result of assembly. The subassembly is then mounted in the body of the tube on the insulator assemblies 33. When proper cathode to anode alignment has been achieved the nuts 32 are tightened down on the fingers 24 to hold the fingers in place.

The tube 1 is then placed in a vacuum bell jar and the cathode structure is again thermally cycled using the cathode heater 37 as the heat source. This final heating is to assure removal of all stresses prior to sealing the tube.

In a typical reverse magnetron tube of the present invention operable at 35 gHz. and utilizing vane resonators 11, the cathode emitter ring 44 has an inside diameter of 1.109" with an anode to cathode spacing of 0.012". The anode-cathode concentricity is maintained within :00005" over a range of radial expansion of 0.003" of the inside diameter of the emitting ring 44. Loss of concentricity between anode and cathode produces uneven heating of the anode resulting in evaporation of the anode, lower efficiency and reduced operating life. Cathode supports constructed in the above manner have permitted extension of the operating life of the tube to in excess of 2400 hours.

Referring now to FIG. 5 there is shown the ranges of vibration over which the tube of the present invention, as compared with that of the prior art, will be non-microphonic. Non-microphonic in this case means that the bandwidth of the output signal down to the 25% amplitude points is within 4.8 mHz. during vibration at a carrier frequency of 35 gHz. and a power output of kw. peak and 150 watts average. Prior to subjecting the tubes to vibration the output spectrum was 2.8 mHz. Wide to 25% points for both the prior art tube, as described in US. patent application 219,702, and the tube incorporating the tie ring 33 of the present invention. Under 5g vibration the output bandwidth, to 25 points, increases due to frequency modulation components. The prior art tube exceeded the allowable 4.8 mHz. spectral bandwidth over that range of vibration indicated by the Xs On the plot of FIG. 5, Whereas only one small region of that range produced excessive bandwidth with the improved cathode spring finger support of the present invention as indicated by the broken region of the solid line.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A reverse crossfield tube apparatus including, means forming an anode microwave circuit for supporting microwave energy thereon for interaction with a stream of electrons, means forming a cathode emitter ring structure concentrically surrounding said anode circuit means in spaced relation therefrom to define a crossed field electronic interaction region in the annular region of space between said anode circuit and said cathode emitter, means forming an evacuated tube structure enveloping said anode and cathode means, means forming a spring support disposed about the circumference of said cathode emitter for supporting same from said tube structure, asid spring support means including a plurality of spring fingers spaced about the circumference of said emitter ring and each having a generally axially directed leg portion, and means forming a tubular metallic tie ring coaxially disposed of said cathode emitter and fixedly attached to and circumferentially interconnecting said axially directed leg p0r- 5. tions of said spring fingers, thereby substantially stiffening said spring support means to suppress certain mechanical resonant mOdes of vibration thereof.

2. The apparatus of claim 1 wherein said spring fingers each include a pair of radially directed foot portions, one of said foot portions being outwardly directed and the other being inwardly directed, with said axially directed leg portion being disposed therebetween, means forming a plurality of axially directed insulator assemblies affixed to said tube structure at points around the circumference of said cathode emitter ring structure, and wherein said outwardly directed foot portions of said spring fingers are fixedly secured to said insulator assemblies.

3. The apparatus of claim 2 wherein said inwardly directed foot portions of said spring fingers are fixedly secured to said cathode emitter ring structure forming the point of attachment therebetween.

4. The apparatus of claim 1 wherein said tie ring is tubular and is substantially axially coextensive with at 6 least 75% of the axial length of said axial leg portions of said spring fingers.

5. The apparatus of claim 1 wherein there are at least five spring finger supports spaced about the circumference of said cathode emitter ring structure.

6. The apparatus of claim 1 wherein said spring fingers and said tie ring are made of molybdenum and are fixedly attached together by a metal 'braze.

References Cited UNITED STATES PATENTS 3,255,377 6/1966 Sylvernal 3l539.75

HERMAN KARL SAALBACH, Primary Examiner.

SAXFI'ELD CHATMON, JR., Assistant Examiner.

US. Cl. X.R. 

